Field of the Invention
The present invention relates to a technique for controlling an air-fuel ratio of an internal combustion engine in which an exhaust purification device containing a three-way catalyst is arranged on an exhaust passage.
Description of the Related Art
In recent years, exhaust purification devices are disposed on exhaust passages of internal combustion engines for the purpose of purifying nitrogen oxides (NOX) contained in exhaust gases of the internal combustion engines. However, in some cases, nitrous oxides (N2O) may be generated in the course of purifying NOX with the exhaust purification devices.
As one method for restraining generation of N2O, proposed is a method that, in a configuration in which an exhaust purification device contains NOX storage reduction (NSR) catalyst, reduces the amount N2O to be generated at the NSR catalyst by raising the temperature of the NSR catalyst or decreasing the concentration of oxygen in exhaust gas once the amount of N2O flowing out of the exhaust purification device measures a predetermined amount or more (Japanese Patent Application Laid-Open No. 2004-211676, for example).